1. Field of the Invention
This invention relates generally to controlling the pumping rate of a pump of a petroleum well. Specifically, one or more implementations of the invention relate to controlling the pumping rate of a progressing cavity pump in order to increase liquid production from a petroleum well while avoiding operation of the well in a pumped-off state.
2. Description of the Prior Art
Prior art pumping systems for recovering petroleum from underground formations have generally had pumping capacities in excess of the productivity rate of the petroleum formation. This results in a well state in which the well may be pumped dry, i.e., the well production is pumped off, thereby potentially causing damage to the pumping system.
It is well known in the art to provide control systems, such as those disclosed in U.S. Pat. Nos. 4,973,226; 5,064,348; and 5,167,490, to avoid a pumped-off state in a petroleum well in which oil is pumped from the well through the use of a downhole liquid pump actuated by a rod and reciprocated from the well surface by a prime mover. In addition to these reciprocating sucker rod type of pumps, progressing cavity pumps (PCP) are also presently in use in which a rotor is rotated inside a stator for pumping liquids. Progressing cavity pumps are advantageous, because the initial cost of the installation is low as compared to reciprocating pumps. However, the progressing cavity pump may also cause a pumped-off state resulting in potential damage to the pump. Such pump damage is expensive to repair, because the progressing cavity pump must be removed from the petroleum well.
U.S. Pat. No. 5,782,608 describes a method and apparatus for controlling the speed of a progressing cavity liquid well pump by driving the pump with a variable speed drive while measuring the amount of liquid production from the pump. One or more of the implementations described herein are improvements upon the method and apparatus disclosed in U.S. Pat. No. 5,782,608, which is incorporated herein by reference.
3. Identification of Objects of the Invention
An object of the invention is to accomplish one or more of the following:
Provide a system and method of controlling the pumping rate of a progressing cavity pump in order to increase liquid production from a petroleum well while avoiding operation of the well in a pumped-off state;
Provide a system and method of controlling the pumping rate of a progressing cavity pump by varying the speed of the pump, either upwardly or downwardly, by a variable speed drive while measuring the liquid production rate in order to increase liquid production from a petroleum well while avoiding operation of the well in a pumped-off state;
Provide a system and method of controlling the pumping rate of a progressing cavity pump by varying the speed of the pump, either upwardly or downwardly, by a variable speed drive while measuring the pump efficiency in order to increase liquid production from a petroleum well while avoiding operation of the well in a pumped-off state;
Provide a system and method of routinely challenging the current pumping rate of a progressing cavity pump by varying the speed of the pump, either upwardly or downwardly, by a variable speed drive in order to increase liquid production from the well while avoiding operation of the well in a pump-off state; and
Provide a system and method of controlling the pumping rate of a progressing cavity pump by varying the speed of the pump in order to remove sand along with the liquid production;
Other objects, features, and advantages of the invention will be apparent to one skilled in the art from the following specification and drawings.